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              <h1>🛠 Simple CSS+JS dynamic <code>max-height</code> accordions!</h1>

<h2>⚠️ The problem with <code>max-height</code> accordions</h2>
<p>I love the technique of using <code>max-height</code> to create accordions. <strong>Buuuuut</strong>, a big caveat is you can't transition between a <code>max-height</code> of <code>0</code> and <code>auto</code>. Leaving you to either:</p>
<ol>
  <li>Use something like <code>max-height: 999em</code> to account for the tallest content length possible. This causes your opening and closing animations to be too quick.</li>
  <li>Use a smaller value for <code>max-height</code>, but what if your content is too large and it "cuts off" part of it?</li>
</ol>

<h2>💪 transitionend to the rescue!</h2>
<p>You can add a <code>transitionend</code> eventListener to the accordion body (part that opens and closes) to dynamically calculate the <code>max-height</code> value! This event fires after a CSS transition completes. Meaning:</p>
<ul>
  <li>When the accordion is closed the content is positioned absolute so we can hide the content, but still get the <code>scrollHeight</code> value</li>
  <li>When clicking a closed accordion we, store the <code>scrollHeight</code> in a variable and briefly set the <code>max-height</code> to <code>0</code>. We then immediately set the <code>max-height</code> to the value of the <code>scrollHeight</code> on the absolutely positioned element.</li>
  <li>Once the transition is complete we remove the <code>max-height</code> so the content isn't capped at this value. Otherwise, if you resize your browser you might have overflow issues.</li>
  <li>When a user closes the accordion we immediately capture the height again, set the <code>max-height</code> to this value briefly and finally change the <code>max-height</code> back to <code>0</code> to close the accordion seamlessly.</li>
</ul>


<h2>🎉 Demo</h2>
<div class="Accordion" data-accordion>
  <div class="Accordion__title" data-title>
    <h3>Example Heading</h3>
  </div>
  <div class="Accordion__content" data-content>
    <p>Lorem ipsum dolor sit amet consectetur, adipisicing elit. Aperiam tempora voluptatum eligendi rem molestias numquam totam dignissimos animi ullam a culpa modi soluta, vero quisquam vel similique quibusdam neque nam?</p>
    <p>Ipsam dolorem ut similique ullam architecto eum corrupti dolor laboriosam neque error iure aliquam, inventore esse nemo, nisi laborum eaque, est officiis rem id. Doloremque velit excepturi eos tempore neque?</p>
    <p>Pariatur eius harum, quidem cumque corporis ipsa odio quo at, fugit atque inventore sit accusamus dolor unde? Porro ab nihil maxime sunt quasi? Asperiores animi, consectetur provident a aspernatur totam.</p>
    <p>Corrupti, voluptatem! Rem eveniet labore itaque velit amet vel sapiente qui harum quaerat aliquam veniam molestiae, corporis optio molestias magnam, nihil unde! Tempore voluptatem, quaerat sit neque repellat dignissimos earum?</p>
  </div>
</div>

            
          
!
            
              .Accordion {
  border: 1px solid #ccc;
  border-radius: 5px;
  padding: 1rem;
  position: relative;

  &__title {
    cursor: pointer;
    user-select: none;
  }

  &__title h3 {
    margin: 0;
  }

  &__content {
    overflow: hidden;
    transition: .2s max-height;
    will-change: max-height;
  }

  &.is-hidden &__content {
    position: absolute;
    opacity: 0;
    visibility: hidden;
  }
}


/*
 * Demo stuff
 */
body {
  padding: 2rem;
  line-height: 1.5;
}

code {
  background: #4A484C;
  color: #fff;
  border-radius: 5px;
  padding: 0 8px;
}
            
          
!
            
              class Accordion {
  constructor($el) {
    this.$el = $el;
    this.$title = this.$el.querySelector('[data-title]');
    this.$content = this.$el.querySelector('[data-content]');
    this.isOpen = false;
    this.height = 0;

    this.events();
    this.close();
  }

  events() {
    this.$title.addEventListener('click', this.handleClick.bind(this));
    this.$content.addEventListener('transitionend', this.handleTransition.bind(this));
  }

  handleClick() {
    this.height = this.$content.scrollHeight;

    if (this.isOpen) {
      this.close();
    } else {
      this.open();
    }
  }

  close() {
    this.isOpen = false;
    this.$el.classList.remove('is-active');
    this.$content.style.maxHeight = `${this.height}px`;

    setTimeout(() => {
      this.$content.style.maxHeight = `${0}px`;
    }, 1);
  }

  open() {
    this.isOpen = true;
    this.$el.classList.add('is-active');
    this.$el.classList.remove('is-hidden');
    this.$content.style.maxHeight = `${0}px`;

    setTimeout(() => {
      this.$content.style.maxHeight = `${this.height}px`;
    }, 1);
  }

  handleTransition() {
    if (!this.isOpen) {
      this.$el.classList.add('is-hidden');
    }

    this.$content.style.maxHeight = '';
  }
}

/*
 * Instantiate a new Accordion
 */
new Accordion(document.querySelector('[data-accordion]'));
            
          
!
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